A PCB Design Process From Request to Release

A PCB design process is less about the layout tool than about the sequence of checks that turn a schematic into a manufacturable board. Boards fail not because the routing was technically difficult but because the inputs were incomplete, the key nets were never identified, or the output was generated from a version that had already been superseded. A defined process removes those failure modes.

What the Design Request Should Contain

The process starts before the layout. The request should include a reviewed and correct schematic, a bill of materials with part numbers that the purchasing system recognises, and a mechanical drawing that defines the outline, the mounting holes and their positions, the connector positions and any keep-out area. Where the design uses a component that has no part number yet, the footprint has to be provided and verified, because a footprint created from a datasheet drawing without checking is the most common source of a board that does not fit.

Requiring those inputs before the layout begins is not bureaucracy. Each of them is expensive to obtain later, and each of them changes the layout if it arrives after routing has started.

Understanding the Requirements Before Placing Anything

The first engineering task is to read the schematic for its electrical requirements rather than its connectivity: the operating frequency of the analogue sections, the edge rates and clock speeds of the digital sections, and the parts of the circuit that are sensitive to noise. This is what determines which nets are critical.

The second task is to identify those critical nets explicitly, together with the components that drive them. Power, clocks, high-speed buses and any net with a controlled impedance requirement belong on the list, and the list is what the rest of the layout is organised around. Where the schematic violates the design rules of the project, the issue should be raised and resolved at this stage rather than routed around.

A Written Plan With Checkpoints

The plan should name the checkpoints rather than only the deliverable: netlist import, placement complete, routing complete, signal integrity review complete, manufacturing output generated. Each checkpoint is a point at which the design can be reviewed against a stable state, and each has an owner. A plan that only names a delivery date has no place to catch a problem.

The plan should also be agreed between the designer and the engineer who owns the schematic. That agreement is what makes it legitimate for the designer to stop work when the inputs change, and it prevents the situation in which the layout is completed against a specification that has already moved.

Netlist, Footprints and the Board File

The netlist is the interface between the schematic and the layout, and its correctness and completeness should be established before anything else. The format has to match what the tools expect, and errors introduced by the schematic capture should be resolved at the source rather than patched in the layout.

Component footprints should be confirmed at the same time, with each one checked against the manufacturer drawing for pad dimensions, pitch and the position of pin one. The board file itself starts from the mechanical drawing, using a defined origin. Setting the origin deliberately, rather than accepting whatever the tool provides, makes every subsequent dimension and every assembly drawing reference the same point.

Placing, Routing and Reviewing

Placement is where the electrical requirements and the mechanical constraints meet. Components that belong to one functional block should be placed together, connectors should follow the mechanical drawing, and the critical nets identified earlier should be placed so that they can be routed with a continuous reference. The placement review checks that the mechanical constraints are met and that the power distribution and decoupling are sensible before routing begins.

Routing then proceeds from the critical nets inward, with the impedance-controlled and length-matched groups routed first, because they have the least freedom. The review at this stage examines the return paths, the reference continuity and the separation between noisy and sensitive groups, which are the aspects that cannot be corrected by adjusting a width afterwards. Our high-speed design rules notes describe the checks that apply, and the layer assignment guidance explains the stack-up decisions that support them.

Significance of the Output Stage

The final stage produces the manufacturing data: the routing layers, the silkscreen and mask layers for both sides, the drill file and the mechanical layer that defines the outline. Each of those should be verified against the released stack-up, and the verification should be recorded. The most common cause of a wasted fabrication run is not a routing error but an output generated from a design file that was edited after the check.

An assembly drawing and a fabrication note belong with the output, as does the version of the design they correspond to. Our fabrication notes guidance lists what the note should contain, and the design release checklist covers the review that closes the process.

Version Control and Change Handling

The most damaging failure in a design process is a change that is applied to one artefact and not to the others. A schematic is revised, the layout is updated, and the fabrication note still describes the previous stack-up. Version control addresses this by treating the schematic, the layout, the bill of materials and the manufacturing note as one release, identified by a single revision, and by requiring that any change produces a new revision rather than an edit to the current one.

Change handling follows from the same idea. A late change request should be assessed for its effect on the critical nets, the placement and the stack-up before it is accepted, and the assessment should be recorded. Changes that affect only the silkscreen cost nothing; changes that move a component on a controlled-impedance net can invalidate work that has already been reviewed. Making that distinction explicit is what keeps a late change from becoming a late failure.

FAQ

Why insist on a reviewed schematic before layout starts? Because a schematic change after routing begins invalidates work in proportion to how far the layout has progressed. A change that adds a component affects placement and routing; a change that alters a net affects the netlist and possibly the layer assignment. Resolving those changes before the layout starts is cheaper by a wide margin, and the review is what makes that possible.

How much of the process applies to a small board? All of it, in proportion. A two-layer board with a modest component count does not need a formal signal integrity analysis, but it does need the input checklist, the critical net list and a review before release. The value of the process is in the sequence rather than in the ceremony, and the sequence applies at every scale.

What does gopcb need to start a layout? A schematic that has been reviewed, a bill of materials, a mechanical drawing with the connector and mounting positions, and the footprint for any new component. With those in hand the plan can be written and the checkpoints defined. Designs that arrive without them usually lose more time in clarification than the clarification would have taken at the start.